In recent years, in accordance with development of functions of electronic equipment, wiring boards with extremely high wiring density are desired. As such wiring boards with high wiring density, there is a wiring board in which a wire is used for necessary wiring. Hereinafter, an electric wire used as wiring will be referred to as a ‘wire,’ and a wiring board in which the electric wire is used as wiring will be referred to as a “multi-wire wiring board.”
A multi-wire wiring board is manufactured by, after forming an adhesive sheet (adhesive insulation layer) having adhesive property on an inner layer substrate on which circuits such as a power supply layer and a ground layer are formed, wiring (making a wire adhere with ultrasound while making the wire run on the adhesive layer) a wire coated with a polyimide resin, or the like, using a numerical control wiring machine, fixing the wire through lamination, or the like, making a through-hole which crosses the wire, and performing electroless metal plating on inside of the through-hole. As the insulated coated wire used in this multi-wire wiring board, an insulated coated wire having a wire, a wire coating layer disposed around the wire, and a wire adhesive layer disposed around the wire coating layer, is used (see, e.g., Patent Literatures 1 to 4).